THE USE OF MUSCLES IN THE BODY 



121 



of the point of application of the power. In the Body the power- 

 arm is usually very short so as to gain speed and range of move- 

 ment, the muscles being powerful enough to do their work in spite 

 of the mechanical disadvantage at which they are placed. The 

 limbs are thus made much more shapely than would be the case 

 were the power applied near or beyond the weight. 



It is of course only rarely that simple movements as those 

 described above take place. In the great majority of those 

 executed several or many muscles co-operate. 



The Loss to the Muscles from the Direction of their Pull. It 

 is worthy of note that, owing to the oblique direction in which 

 the muscles are commonly inserted into the bones, much of their 

 force is lost so far as producing movement is concerned. Sup- 

 pose the log of wood in the diagram (Fig. 52) to be raised by pull- 



Fio. 52. Diagram illustrating the disadvantage of an oblique pull. 



ing on the rope in the direction a; it is clear at first that the rope 

 will act at a great disadvantage; most of the pull transmitted 

 by it will be exerted against the pivot on which the log hinges, 

 and only a small fraction be available for elevating the latter. 

 But the more the log is lifted, as for example into the position 

 indicated by the dotted lines, the more useful will be the direction 

 of the pull, and the more of it will be spent on the log and the 

 less lost unavailingly in merely increasing the pressure at the hinge. 

 If we now consider the action of the biceps (Fig. 39) in flexing the 

 elbow-joint, we see similarly that the straighter the joint is, the 

 more of the pull of the muscle is wasted. Beginning with the arm 

 straight, it works at a great disadvantage, but as the forearm is 



